Image reproducing device



Feb. 16, 1960 l D. w. DAVIS IMAGE REPRODUCING DEVICE Filed April 26, 1.954

' 2 Sheets-Sheet 1 FIG.4

INVHVTOR. DEAN W. DAVIS 220 22c 22 22g 22i 22b 22d 22f 22h Feb. 16, 1960 D. w. DAVIS 2,925,525

IMAGE REPRODUCING DEVICE Filed April 26. 1954 2 SheetsSheet 2 INVENTOR. DEAN W. DAVIS AT TORNE Y 2,925,525 iMAGE REPRODUCING DEVICE D'ean Davis, Fort Wayne, Ind., amignor to Internatronal Telephone and Telegraph Corporation Application April 26, 1954, Serial No. 425,559

6 Claims. (Cl. 315-) The present invention relates to an image-producing dev ce and more particularly to an apparatus for reproduclng radiation images on a viewing screen.

ThlS invention contemplates the utilization of a dielectric material or phosphor which is excitable to luminescence by the application of a variable electric field thereto. A typ1cal suitable material known in the art to' which this invention appertains is a copper activated zinc oxide and zinc sulphide mixture as explained by Destriau in the 1937 edition, volume 38, of Philosophical Magazine on pages 700-739, 774-793 and 800-887, and has been characterized as electroluminescent. One method of exciting this material is to apply a variable A.C. voltage to two opposite electrode plates having the electroluminescent material therebetween, the resulting structure resembling that of a simple parallel plate condenser.

Several applications have been submitted to the art as being practical, which include, among others, use in illuminating lamps and in' radiation amplifiers such as that disclosed in Orthuber et al. application Serial No. I

385,802, filed October 13, 1953, now Patent No. 2,837,660.

play device for producing radiation images.

It is another object of this invention to provide a radiation display device composed of an electroluminescent phosphor viewing screen and an image signal control device electrically coupled to but physically separated from said screen, the control device serving to apply image information to the screen for display reproductio by the latter.

It is still another object of this invention to provide an image screen using an electroluminescent phosphor panel which converts voltage differences into light output, such voltage differences being applied'to said panel in spaced discrete elemental areas corresponding to elements of an image to be reproduced.

In accordance with the principles of this invention, an image reproducing device is provided which includes an electroluminescent phosphor panel contained between electrode members which apply control voltages to ele-' mental areas of the panel in accordance with an image which is to be reproduced. The control voltages are sup- In the drawings: a

Fig. 1 is a diagrammatic sectional illustration of one voltage-varying apparatus which may be used in control-' ling the i'eproduction of an image by an electroluminescent phosphor screen; a

Fig. 2 is a sectional illustration of a varying apparatus used in conjunction with the device of Fig. 1 for reproducing the aforementioned image;

Fig. 3 is an elevational view of the devices of Figs.

1 and 2;

Fig. 4 is a perspective illustration of an electroluminescent phosphor screen in diagram form;

Fig. 5 is a partial sectional view of Fig. 4;

Fig. 6 is a circuit diagram used in explaining the operation of this invention;

V Fig. 7 is a diagrammatic illustration of another type of voltage-varying apparatus for controlling potentials applied to the screen of Figs. 4 and 5; and

Fig. 8 is a circuit diagram used in explaining the operation of the device of Fig. 7.

With reference to the drawings, and more particularly to Fig. l, a conventional cathode ray tube 1, commonly characterized as a flying spot tube, is coupled into .a f

conventional television display circuit which includes the usual deflection coil 2 and focusing coil 3. A suitable saw-tooth voltage wave occurring at the rate of, for example, cycles per second, is applied to the coil '2 for deflecting the cathode ray beam 4 in a straight line b a 1 strikes the screen 5, itproduces a spot of light. As the beam is scanned over the screen, this spot moves corre- I spondinglyyhence, the tube is commonly characterized path over'the usual phosphor screen 5. As the as producing a flying spot of light.

Impedance-changing means which is sensitive to the 1 spot of light is generally indicated by the reference numeral 6 and is comprised of a transparentglass rein-f forcing plate 7, a transparent conductive coatlng or electrode 8, a layer of photoconductive material 9, and a plurality of spaced electrode elements or members 10. The photoconductive layer 9 is laid in contact with the electrode film 8 and may comprise the usual crystalline V cadmium sulphide material which changes in resistance or impedance in accordance with variations in light energy impressed thereon.

sist of ordinary lengths of wire laid in contact w th the layer 9 and spaced apart in parallel relation substantially as shown. The particular spacing between'these elements 10:and'the character-of the elements themselves W111 become apparent from the following description. The

elements obviously may take different forms than that illustrated.

The light spot produced by the tube 1 is focused by means of a simple lens 41 through the glass plate 7 and film electrode 8 onto the photoconductive layer 9m such a manner that the photoconductive material is scanned.

- on the side opposite thevelectro de elements '10.

plied to the electrode members by means of a voltage; V:

varying apparatus controlled to produce different voltages of which are disclosed and described in'detail hereinafter. p,

Generally, onedevice utilizes a photoconductive material for varying the voltages applied to the electroluminescent panel, and the other device utilizes an electron beam for accomplishing the same end. I

For a better understanding of the invention, together with other and further objects thereof, reference ismade 1 to the following description, taken in connection with the accompanying drawings, the scope of the invention being The control device 6 is generally in strip-like form and V infront elevation appears as illustrated in F1g. 3. As will! nowbe apparent, the spot of 'lightproduced by thetube 1 is scanned from end to. end of'the'strip. r

Withreference to Fig. 2, it be. notedthata sys- 1 tennis provided'which appears in diagram form tobe I substantially identicalto that illustrated in Fig. 1. In '1 the reproductionof a television image by means of the 1 conventional scanning techniques, the arrangement of. a

" Fig. '1. is the vertical or low frequency scanning system whereas that of Fig. 2 is the horizontal or high frey quency system. The. exact details of ,construction willlac-further explained inthe following.

The flying spothtubev 11 as'well as the associated X deflecting and scanning c'oilslZ. and 13 are substantiallyv Patented Feb. 16,1960.-

similar voltage- The electrode elements 10 may con the" same as the tube 1' and its associated coils. The principal differen'cebetween the two tubes and" the associated coils is that the tube is operated at the usual vertical scanning rate of 60 cycles per second, whereas the tube 11 is operated at the usual horizontal scanning rate of" 15,750 cycles per second. It willh'e apparent that these scanning rates areconventional in the televi sioir art.

A strip-like voltage-controlling device 1'4 which may be substantially identical to the device 6' of'Fig. 1' is composed'of a glass plate 15; a transparent electrode film 16'. and a. layer of photoconductive material 17. The electrode elements 18 mounted on the photocondhctive, layer 17 correspond to the elements of Fig, 1. Fig.3 is a. front'elevation of the voltagevcontrolling device l4'and shows the conductive, electrodes 18 mounted. thereon in spaced parallel relation. The left-hand ends of these elements 1'8 are, in the illustrated embodiment, mere wire. extensions of the elements 18-which are coupled-to, an electroluminescent phosphor panel as will be. explained. in more detail in the following.

As explained earlier, the voltage-controlling device 6 of Fig. l in front elevation looks substantially thesame. as that illustrated in Fig. 3. For all practical purposes the two devices 6'and 14 may be identical in construction. The film electrode 8 of the device 6 is grounded as illustrated and the electrode. 16 of device 14. is. con. nected to a suitable. source. of positive voltage asillusr trated.

Referring now to Figs. 4 and.5, the,electr.oluminescent. phosphor panel, is illustrated as. being composedzof athina layer 19 of phosphor material which. is substantially flat.

andof suchwidth and. length. as. would be, desired ima.

television viewing screen. Electrode. meansare. applied. to'oppositesides. of the. panel 19 for applying controlling, voltages thereto to cause the latter to luminesce. in. a.v predetermined manner. This electrode means-is; composed of a..reticulate screen or the like having-.bare wire. conductors extending in one direction and. insulated. strands of the same wire or a plastic matcriaL extending, transversely thereto. Thisscreen is illustrated as being substantially similar to ordinary fine mesh. screen-which is conventionally used rn'the'art. As willzbe. observed: more clearly in Fig. 5, the screen applied to: the left= hand face of the panel 19'is. composed of' wires Zil-and. insulated strands 21, and the screen. applied tothe righthand face is composed of similar wires 22 and insulated strands 23. The wires 20 and 22 preferably extend. indirections at right angles to each other as is. illustrated. in the perspective View of Fig. 4.

As will be seen in Fig. 5, the individual-wires 20 and" 22'pass alternately over and underthe respective insulated strands 2 1- and 2.3-such-that the wires have spaced point contacts with the respective panel faces, for example, as at 2420s: the. left-hand face and 25 on the right-hand face.

In a practical embodiment: of this. invention, there are-- preferably 500- such wires 2% and 2-2 suitably spaced apart in parallel relation on the respective facesrofthe. panel 19' in order to provide an arrangement which will produce a number of picture elements corresponding; to the operative capabilities of present television display: devices. For example, it isestimated that present'daytelevision tubes will provide iinages composedofi approximatelyZSOiOOO elemental image areas, and. from. the foregoing it will be apparent that by the use: of 500; conductive wires on opposite sides of the phosphor; panel. 19'; this same number of image areas. may be. obtained. Of: course, it is obvious that as the screen is' enlarged, theznumber of wires 26* and 22 which-maybezu'secb may besnbstantially increased per unit area: of the screen such; that more elemental image areas may be obtainech than. is considered practically feasible today. Y

All; 01% the wires. 20 are provided. with: connectingzl'ead's:

20a through 20g as illustrated, and similarly the wires 22 are provided" with connectihg' leads 22d through 221'." These respective connecting leads extend over to the voltage-controlling devices of Figs. 1 and 2 in a suitable manner such as, for example, the leads 20a through 20g being connected to the electrode elements 10 in the order indicated by the reference symbols 2011a through 20gg. The connecting leads 22a through 221' are in turn connected to the electrode elements;- 18 of Fig: 2 in the order indicated by, the reference. symbols.22aa through.-

with all. of. the photoconductive and. phosphor assermblies 6; 1.4 and. 19.. Under noelight conditions (i.e-:,, the photoconductive assemblies6-and ltofIFigs. l. and'zZir are. contained inside. a. completely darkened. enclosure} the'voltage V1, ofbattery. 26. will be distributedoverthe:

impedance. elements, 17,..19, and 9 of, Fig. 6 in the maltener illustrated, the; voltage V2 appearing across the.- photoconductive.elements.17,,the voltage V3 appearing over the. corresponding elemental, areatof the; phosphor" panel, 19. and.the voltage.:VI41 appearingover the -photoconductive element. 9. Stated; in:= other words; the: sum,

of the vo1tages.V2 ,..V3.and V flwillequalthe batterytz voltage. V1.

If it were possible torcompletely short out. therphcto.- conductive element or.impedance:9:(.-Fig;. 6) by. means; oft a switch 27-, thefullvoltage of the battery-'26- would be,

impressed. over the.tworimpedanceelements-17 and; 19;- This would produce a redistribution of voltages across the. respective. impedanceelements- 1,7- and, 19. This-re.- distribution would. occur, obviously, immediately upon-1 closure: of the switch 27.' such that a voltagechangeor variation would: occur. betweenthe two conductors Ziland; 22,..for example, which embrace the phosphor. impedance.

19. This phosphor having the characteristieas explained.v

earlier, that. it luminesces upon-being excited by a variable; potential, it is seen that. that portion of the phosphors material 19 between the two conductors 20 and22 will;

produce light provided that impedance 17 issmall compared to impedance 19 such that voltage V3 exceeds the: threshold voltage required-to produce luminescence; By: alternately opening and closing the switch- 27,- the; e1 mental area of the. phosphor panel 19' shown inFig. 6' may be caused to luminesce.

Theshorting elfected by' the switch 27 isactually. produced by the-spot of light producedrby the tub'.Qf:Eig; 1. By directingthis spot of lightontothe photoconductive layer. 9 at a point just opposite. the, topmost electrodeelement 10 specifically indicated by the referencesymhoh 20m, the resistance of the photoconductive. materialfbe; tween the electrode 8 and the element 10 will; immediately lower. This resistance is negligibly small. with intense light, thus" resembling a short" circuit. Switching the spot of light on and oif'thus-re'sembles opening and'closing the switch 27 of Fig. 61 By scanning; an intense spot: of light from one end ofthephotoconductivcassembly 6 to theother, the spot'will alternately registerin='succession with the respective electrode elements 10 in-the sequence 2012a, 20kb, etc., through 20gg. Since theseelements 10 are connected to the parallel wires..2,0:on. thephosphor panel 19, it is seen. that. these wires 20m sequentially: grounded. as. the. spot of lights. in; tube: 1% (Fig. 1). registers with; the. respective electrodes: elo ment. 1!).

Assuming that the spotc' of; light: by when is stationary on the layer 9 in registry with the electrode element 20aa, variation in the intensity of the spot from tube 11 (Fig. 2) trained on the photoconductive layer 17 just opposite the electrode element 22aa will serve to produce a variation in the resistance between the electrode film 16 and this element 22aa. Hence, the equivalent resistor 17 of Fig. 6 is indicated as being variable. By varying this resistance 17 (Fig. 6) the voltage applied to the phosphor element 19 correspondingly changes, causing the latter to luminesce in corresponding changing brightness. By modulating the beam of light produced by the tube 11 of Fig. 2 with video information, the corresponding elemental area of the phosphor panel 19 is caused to luminesce according to such information.

Having now explained how controlled voltages are applied to opposite sides of the phosphor panel 19, it will be apparent that by scanning the spot of light of Fig. l at the usual 60 cycle vertical scanning rate and the spot of light of Fig. 2 at line scanning frequency or 15,750 cycles per second, the result will be an application of exciting voltages to elemental areas of the phosphor panel 19 in a manner which corresponds almost exactly to that of the scanning action of a cathode ray beam in a conventional picture tube. Essentially, the spot of light from tube 1 excites wire 20a while the spot from tube 11 scans over all of the wires 22a through 22i. Where the respective wires 20a and 22a cross on opposite sides of the phosphor panel 19, an exciting voltage will be applied to the latter to produce corresponding point luminescence. By analogy, connecting a voltage to one wire 20 and one wire 22, only the point or elemental area in the phosphor panel 19 where these wires cross will luminesce. Thus it is seen that scanning the wires 20a through 20g at a vertical scanning rate and the wires 22a through 22i at a horizontal scanning rate serves to produce the usual television scanning field or frame.

By alternating the connections between the wire elements 20 as shown in Fig. 4, it is possible to obtain interlaced scansion.

From the foregoing, it will appear obvious that other expedients are available for applying the necessary control voltages to the opposite sides of the phosphor panel 19. An example of such an alternative arrangement is shown in Figs. 7 and 8 wherein a cathode ray tube is provided with a plurality of tiny electrode targets indicated by the reference numeral 27a. Two such cathode ray tubes are used, one tube being connected to the horizontal extending wires 20 and the other tube being connected to the vertical wires 22. Each target electrode 27a is connected through a suitable fixed resistor 28 to a source of B supply voltage at the terminal 29, there being one target 27a for each wire 20, 22. Thus, with an electron beam issuing from the cathode 30 which is grounded, a current is produced through the impinged target and the respective resistor 28. This current in turn produces a voltage drop over the respective resistor 28 which may be applied to the various wires 20 and 22 from suitable terminals indicated by the reference numerals 31, 32, 33, 34, 35, 36 and 37. Connecting all these terminal points 31-37 to the leads 20a-20g will serve to provide a control voltage for the horizontally extending wires 20 and connecting a similar set of wires from another cathode ray tube to the other set of wires 22 will serve to apply the necessary control voltages to the other side of the phosphorpanel. The beam issuing from the cathode 30 may be modulated in the conven-'- tional manner and scanned in a rectilinear path-over the example, incandescent material 'or; fluorescent gas'may beg used as the light-producing medium. Further, the

voltage difference between two'wires may control the position of tiny elemental shutters which control transmission or reflection of light.

In explaining the operation of this alternative em'- bodiment, reference is made to Fig. 8 wherein the equiva lent circuit diagram shows the electron beam as corresponding to the variable resistor 38. The electron beam of the other cathode ray tube is indicated by the variable resistor 39. Other parts of the diagram bear reference numerals which correspond to corresponding parts of the.

physical construction.

By switching the resistor 39 alternately into and out of the circuit by means of the electrode switch 49, it is seen that the voltage between the two elemental electrodes 20 and 22 of the phosphor panel 19 can be correspondingly changes to cause the latter to luminesce..

With the switch 40 closed as illustrated, the resistor 38 (electron beam) when modulated will serve to vary the potential at terminals 31-37 to produce corresponding voltage variations between the two panel electrodes 20 and 22.

By scanning the beam 38 over all the target electrodes 27a at one scanning rate and modulating this beam with video information, and scanning the beam 39 (Fig.8)

over its electrodes at the other scanning rate, it will be seen that voltages may be applied to the elements of the panel 19 in the samemanner as explained in connection with the preceding embodiment.

Having explained two dilferent modes of applying picturecontrol voltages to the phosphor panel 19, alternative apparatus will be apparent to a person skilled in the art,

which will not depart from the scope of this invention. -Such an alternative apparatus serves tomodulate both tubes 1 and 11, and both beams 38*and 39 with video information in opposite respectivephase thereby doubling the potential differences between the crossed phosphor electrodes 20 and '22. This serves to increase picture brightness; Practical design desiderata will determine which alternative arrangement is preferred...

What is claimed is:

1. An image-reproducing device comprising phosphor,

material supported in sheet-like 'form, said material luminescing upon the application of a varying electrical field thereto, electrodes contacting opposite sides of said phosphor sheet, said electrodes comprising a plurality of wire-like elements, the electrode elements on each respective side being spaced apart and extending in essentially the same direction, the electrode elements on opposite sides ofxsaid sheet extending in directions transverse to each other, and voltage control means operatively member being electrically coupled to respective onesof said electrode elements on opposite sides of said phosphor sheet, .and means for applyingfvoltage to both photoconductive members 'in such a manner that the photoconductive material, the electrode elements, the electrode 1 members and said phosphor sheet are connected in series. 2. An image-reproducing device comprising phosphor material supported in sheet-like form, said material luminescing'upon the application of a varying electrical field thereto, electrodes contacting opposite sides of said phosphor sheet, said' electrodescomprising a plurality of ate-eases wiredilce elements, the electrode elements on each resp'ective sidebeing spaced apart and extending in essential ly the samedirection, the electrode elements on opposite sides ofsaid sheet extending in directions transverse to each other, voltage control means operatively coupled toallof said electrode elements such that only one element orreach sheet side will have voltage applied thereto simul' taneously, said voltage control means comprising two radiation-sensitive devices, each device comprising a member composed of photoconductive material whichvaries in impedance in accordance with varying radiation impressed thereon, a plurality of spaced electrode members mounted on each p-hotoconductive member, thenumber of electrode members on each photoconductive member corresponding to the number of electrode elements on a particular one of said phosphor sheet sides, the electrode members of each photoconductive member being electrically coupled to respective ones of said electrode elements on opposite sides of said phosphor sheet, means for applying voltage to both pho-toconductive members in such a manner that the photoconductive' material, the electrode elements, the electrode members and said phosphor sheet are connected in series, and means for scanning each photoconductive member' with radiation modulated in accordance with an image to be reproduced, said scanning serving to alter the impedance of the respective photoconductive members according to the scanning movement of said modulatedradiation;

3'. An image-reproducing device comprising phosphor material supported in sheet-like form, said material luminescing upon the application of" a varying el'ectrical field thereto, electrodes contacting opposite sides of said phosphor sheet, said electrodes comprising a plurality; of wire-like elements, the electrode elements on each" respective side being spaced apart and extending in essentiallythe same direction, the electrode elements on opposite sides of said sheet extending in directions transverse to' each other, voltage control means operatively coupled to' all of said electrode elements on one side of said sheet and sequential switching means coupled to all" of said electrode elements on the other side of said sheet such that only one element on each sheet side will have voltage applied thereto simultaneously, said voltage control means" comprising a cathode ray scanning device having a plurality of anode electrode members, each of said electrode members being connected to a source of anode potential by a resistor and being connected to a corresponding one of said electrode elements on said one side of said sheet, said scanning device thereby serving to applyvoltages of controllable amplitude to said electrode elements.

4: An image-reproducing device comprising phosphor material supported in sheet-like form, said material luminescingupon the application of a varying electrical field thereto, electrodes contacting opposite sides of said phosphor sheet; said electrodes comprising a plurality of wire-like elements, the electrode elements on each respective. side being spaced apart' and extending in' cssential'ly thesame direction, the electrode elements on'opposite sides of said sheet extending in directions transverse to each-other, voltage control means respectively operatively'coupled toall of said electrode elements on each side of said sheet such that only one elementoneach sheet sidewill have voltage appliedthereto simultaneously, each of said voltage control means comprising a cathode ray scanning device having a plurality of anode electrode members with each of said electrode members being connected to a source of anode potential by a resistor and" beingconnected to corresponding one of' safd elect'rode element'sona respective sideiof said sheet, said scanning devices thereby serving to' applyvoltages of controllable amplitude-to said electrode elements.

5. An image reproducing device comprising: phosphor materialsupported in sheet-like form, said material luminescing upon the application of a varying electrical field thereto, a first woven mesh contacting one side of said phosphor sheet and having parallel strands extending in one direction formed of conductive material and parallel strands of said second woven mesh extending transversely of said parallel conductive strands of said first woven mesh and contacting said phosphor sheet at spaced intervals forming second electrodes, the respective points of contact of said electrodes with said phosphor sheet on opposite sides thereof being in transverse alignment, voltage control means operatively coupled to all of said electrode elements such that only one element on each side of said sheet will have voltage applied thereto simultaneously, and switching means cooperatively associated with said voltage, control means for applying a voltage to said elements in a predetermined sequence.

6. In an image reproducing device: phosphor material supported in sheet-like form, said material luminescing. upon the application of a varying electrical field thereto, a first woven mesh contacting one side of said phosphor sheet and having parallel strands extending in one direction. formed of conductive material and parallel. strands formed as insulators and extending at right angles to. said conductive strands, said parallel conductive strands of said first woven mesh contacting said phosphor sheet and spaced at intervals along their length forming, first. electrodes, a second woven mesh contacting, the other. side of said phosphor sheet having parallel strands extending in one direction formed of conductive. material and parallel strands formed as insulators extending. at: right angles to its parallel conductive. strands,, said parallel conductive strands of said second' woven. mesh extending transversely of said parallel conductive strands of said first woven mesh and contacting. said phosphor sheet at spaced intervals along their length forming. second electrodes, the respective points of contact of said electrodes with said phosphor sheet. on opposite. sides thereof being in transverse alignment.

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